Well, I'm sorry to tell you that it's a complete urban legend. Think about it. The wall may be long (5,500 miles), but it is not that wide (about 20 feet). There are structures much wider than the Wall, and they are not visible from space!*

But here is something amazing that is visible from space. And it is not man-made. It is animal-made. Actually beaver-made.

In 2007, researcher Jean Thie discovered (by accident) a gigantic beaver dam that is about half a mile long (2,800 feet). To appreciate how incredible that is, imagine that the average beaver dam is around 20 feet long. The Alberta dam is twice as long as the Empire State Building, or more than twice as long as Hoover dam, or more than eight football fields long! I guess it's only fair, since it is located in Wood Buffalo National Park, Alberta, which happens to be the largest National Park in Canada.

The record for the world's largest beaver dam was previously held by a 2,100-foot-long structure in Three Forks, Montana.

The dam is located in a pretty much inaccessible part of the park, about 120 miles northeast of Fort McMurray, south of Lac Claire. Which means that, sadly, most interested readers and this author probably won't see the dam in their lifetime.

Significant vegetation is growing on the dam, which indicates that it's an old structure. Scientists believe construction started in the mid-1970s. Multiple families and several generations of beavers have worked on the dam, which serves as protection against predators and as a way to help access food during winter time. Incidentally, a dam dramatically modifies the habitat, which then allows various animal species to occupy new niches.

It is not a beaver dam like most of us imagine it would look. “It is a long but low structure predominately made of mud and reeds and the natural local terrain. The beaver has smartly used these features and materials to achieve this dam and make a habitable environment” explains Mike Keizer, External Relations Manager based in Fort Smith, Northwest Territories.

Beavers have been hunted for their pelts, as well as for castoreum, an exudate from the scent glands. In combination with the beaver's urine, the secretion is used to mark their territory.

Castoreum has been used as an analgesic, anti-inflammatory and antipyretic. Today, castoreum is still used in the perfume industry.

Yupik (Eskimo) medicine used dried beaver testicles like willow bark to relieve pain. Now this is where is becomes interesting: The activity of castoreum has been credited to the accumulation of salicin from willow trees in the beaver's diet, which is transformed to salicylic acid and has an action very similar to aspirin.

* To be fair, it’s more complicated than that. The real question is, what do we define as “visible from space”? How high is the observer?